Fastening clips of the type referred to above, which are sometimes called U-shaped or C-shaped, may be small, separable clips attached to a larger structure, or an integral part of a larger structure that is fastened to something else. I either case, each type has a pair of axially opposed walls joined by a generally perpendicular wall, hence the C- or U-shape. The threaded fastener has a head and tip, with threads, and often a predetermined length that can't be exceeded in the particular application. The fastener passes freely through a first wall, which is ultimately abutted, directly or indirectly, with the fastener head, and the tip passes through a hole in the opposed second wall, the edge of which is engaged by the side threads. This action tends to pinch or bias the walls toward one another as the fastener is tightened. The security or strength of the fastening achieved depends on how well and how securely the side threads of the fastener engage the hole in the second wall.
Prior art clips of the type referred to above often alter the perimeter area around the hole in the second wall to try to improve the fastener operation. Specifically, the perimeter is often formed into a dimpled or conical shape so as to funnel the fastener tip toward the hole edge. This also has the effect of moving the hole edge away from and out of the plane of the second wall, however. If there is a limitation on how long the fastener can be, then the edge of the hole may end up engaging fewer threads, the ones nearer the tip which may be smaller and less effective. Another common technique is to lance or split the thread engaging edge of the hole, which is displaced in opposite axial directions, creating separate edge portions to contact more threads of the fastener. This has two less than desirable effects. 20 The edge is weakened by being split in two, and an asymmetry is created at the split which causes the threaded fastener to pull in unevenly as it is tightened.